The present invention relates to an electrically-conductive, thermally-insulating structure and a method for producing such a structure. In one aspect, the electrically-conductive, thermally-insulating structure relates to a coating which is both electrically-conductive and thermally-insulating. In another aspect, the electrically-conductive, thermally-insulating structure relates to a sheathing which has a base layer and a coating which is both electrically-conductive and thermally-insulating. In yet another aspect, the present invention relates to a device capable of flight having an electrically-conductive, thermally-insulating structure.
Certain apparatuses require a sheathing or a coating which both insulates the apparatus from heat while simultaneously maintaining electrical conductivity across the sheathing or coating. This requirement can be particularly important in missiles and other devices capable of flight, for example, rockets and aircraft. During high speed flight, aerodynamic heating occurs which can cause a significant increase in the temperature of the flight structure. As the contents of the missile and the missile structure are, in some instances, sensitive to high temperatures, they must be thermally protected. Further, it can be important for the outer surface or skin of the missile to be electrically-conductive as antennae or other such devices are often placed on the skin of such missiles and for proper operation must have an electrically-conductive surface path. Additionally, surface electrical conductivity may be desirable to conceal or modify the radar signature of the flight structure.
Accordingly, a need exists for a structure which can both protect the contents of an apparatus from thermal damage while simultaneously maintaining electrical conductivity across the structure.
The present invention is a new and advantageous electrically-conductive, thermally-insulating structure which is capable of protecting the contents of an apparatus from thermal damage due to excessive temperatures exterior to the apparatus while maintaining electrical conductivity across the structure.
In one embodiment, the structure of the present invention is an electrically-conductive, thermally-insulating coating having a thermally-insulating layer with a thermal conductivity of no more than about 3.5xc3x9710xe2x88x923 W/hrxc2x7cmxc2x7xc2x0K and an electrically-conductive layer, applied to the thermally-insulating layer, having an electrical resistivity of no more than about five ohms at 700xc2x0 C. Preferably, the thermal conductivity of the thermally-insulating layer is no more than about 8.7xc3x9710xe2x88x924 W/hrxc2x7cmxc2x7xc2x0K and the electrical resistivity of the electrically-conductive layer is no more than about two ohms at 700xc2x0 C.
In other embodiments, the thermally-insulating layer is made of a silicone-based elastomer or a phenolic-based polymer, for example, a phenolformaldehyde thermosetting polymer or a phenolfurfural thermosetting polymer. Microballoons made of a thermally-insulating material, for example, glass or ceramic, can be dispersed in the thermally-insulating layer to decrease the density of that layer. In one embodiment, the thermally-insulating layer has a plurality of microballoons in the range of about two percent by volume to about 25 percent by volume.
In further embodiments, the electrically-conductive layer is made of a metal, for example, commercially-pure aluminum, an aluminum alloy, commercially-pure copper, a copper alloy, steel, commercially-pure titanium, or a titanium alloy.
Yet further, in one embodiment of the present invention, the thermally-insulating layer has a thickness of at least 1.5 mm and the electrically-conductive layer has a thickness of at least 0.05 mm.
In yet another embodiment, the structure of the present invention is a sheathing for an apparatus having a base layer for providing a base structure to the sheathing and a thermally-insulating layer, applied to the base layer, which has a thermal conductivity of no more than about 3.5xc3x9710xe2x88x923 W/hrxc2x7cmxc2x7xc2x0K. The sheathing further has an electrically-conductive layer, applied to the thermally-insulating layer, which has an electrical resistivity of no more than about five ohms at 700xc2x0 C. Preferably, the thermal conductivity of the thermally-insulating layer is no more than about 8.7xc3x9710xe2x88x924 W/hrxc2x7cmxc2x7xc2x0K and the electrical resistivity of the electrically-conductive layer is no more than about two ohms at 700xc2x0 C.
The thermally-insulating layer and the electrically-conductive layer of this sheathing embodiment have substantially the same properties and are made of the same materials as those of the coating embodiments disclosed herein.
According to yet another embodiment of the present invention, a device capable of flight, for example, a missile, a rocket, or an aircraft, includes a skin capable of enclosing at least a portion of the device. The device has a thermally-insulating layer applied to the skin and an electrically-conductive layer applied to the thermally-insulating layer, wherein the thermally-insulating layer has a thermal conductivity of no more than about 3.5xc3x9710xe2x88x923 W/hrxc2x7cmxc2x7xc2x0K, and the electrically-conductive layer has an electrical resistivity of no more than about five ohms.
Preferably, the thermal conductivity of the thermally-insulating layer is no more than about 8.7xc3x97104 W/hrxc2x7cmxc2x7xc2x0K and the electrical resistivity of the electrically-conductive layer is no more than about two ohms at 700xc2x0 C.
The thermally-insulating layer and the electrically-conductive layer of this embodiment have substantially the same properties and are made of the same materials as those of the coating and sheathing embodiments disclosed herein.
Another embodiment of the present invention is a method for applying an electrically-conductive, thermally-insulating coating to a surface, in which a layer of thermally-insulating material is applied onto the surface and a layer of electrically-conductive material is applied onto the layer of thermally-insulating material.
In one embodiment, the electrically-conductive material is sprayed onto the thermally-insulating layer by either plasma spraying, two-wire arc spraying, or flame spraying.
In a further embodiment, the thermally-insulating material is sprayed onto the surface.
In yet another embodiment, some of the thermally-insulating material is removed to produce a desired contour of the layer of thermally-insulating material. This material can be removed by various processes, for example, sanding or machining.